Traffic calming

One of the most common citizen concerns we hear about is speeding through residential neighborhoods and requests to address that. The City performs traffic counts to document traffic volume and speed data for all neighborhood speeding reports. We then use a combination of police education and enforcement, roadway striping and signage changes to reduce speeds. This is usually effective, but in some cases only for a short while.

In recent years, data showed that additional traffic calming tools were needed in some neighborhoods. Because of a decade-old City policy against installing new speed humps, the City’s Traffic Safety Committee researched other physical traffic calming measures and found traffic circles to be the most effective option. ​

What is a traffic circle?

​Traffic circles are typically between 15 and 25 feet in diameter, placed at intersections of low-speed residential streets to reduce vehicle speeds and traffic cutting through neighborhoods. They are often placed in the middle of existing intersections with minimal changes needed. ​​​

What does the research show about effectiveness for reducing speeds?

​​By forcing traffic to move to the right of the typical lane path, traffic circles effectively lower approach speeds and reduce the number and severity of collisions. The City of Seattle, for example, installed more than 1,000 traffic circles and documented 70 percent fewer collisions.​

​Can emergency vehicles and school buses get through?

​ ​Traffic circles can be designed to meet fire code and provide access to vehicle types necessary within residential neighborhoods. In Marysville, traffic circles were tested using large city vehicles including a fire truck. ​

​How does the City decide where to install traffic circles?​

The Traffic Safety Committee found the need for traffic calming on several neighborhood streets based upon documented conditions. These streets are typically wide, straight/flat neighborhood streets conducive to cut-through traffic and/or speeding.
All roadways evaluated for traffic circles have a posted speed limit of 25 mph. The streets selected all have a larger percentage of drivers traveling well above the posted speed limit. The goal of traffic circle installation is to reduce vehicle speeds through neighborhoods and discourage drivers from using these streets to cut through neighborhoods. ​

​​Where are traffic circles now in place? Are they effective?​

The City has installed three neighborhood traffic calming circles. For the first two, follow-up data shows they have been effective in decreasing both traffic speeds and volumes:

71st Ave NE (64th St NE to Grove St)

Date

Location

Average Daily Traffic​ (ADT)

Average Speed​ (mph)

85% Speed​ (mph)

% of vehicles traveling​more than 10 mph ​over 25 mph limit

Nov 2014​(before)

71st Ave NE​north of ​71st St NE

836

31.0

37.2

17.9

Feb 2016​(after)

71st Ave NE​north of​71st St NE

785

29.8

34.3

11.3

-

# Decrease

51

1.2

2

6.6​

-

% Decrease

6.1%

3.9%

7.8%

36.9%

92nd St NE (State Ave to 51st Ave NE)

Date

Location

Average Daily Traffic​(ADT)

Average Speed​(mph)

85% Speed​(mph)

% of vehicles traveling​more than 10 mph ​over 25 mph limit

Jan 2015​(before)

92nd St NE​west of ​46th Dr NE

2,619

28.6

33.2

8.6

July 2016​(after)

92nd St NE​east of​46th Dr NE

2,382

26.2

30.0

1.6

-

# Decrease

237

2.4

3.2

7.0

-

% Decrease

9.0%

8.4%

9.6%

81.4%

The traffic circle at 56th Ave NE (south of 132nd St NE) was installed in May/June 2016. Before that, average daily traffic was 633, average speed was 37.2 mph, and 15.4% of vehicles traveled more than 10 mph over the 25 mph speed limit. We do not yet have follow-up data for this location. ​

What can those neighborhoods expect?

​​Traffic circle installations are performed by the City Public Works Department and necessary specialty contractors. Each location consists of installation of concrete block curb, a 1-2’ drivable asphalt curb, landscaping, signs and striping. During installation traffic control will be performed as needed, but is unlikely to include full closures or detours. Some work may require traffic flagging for short durations.
​​